Although we don't have to comply with SOX and friends, yet, I think this would be a great Zimbra feature. And a potentially selling point to larger corporations. The advantage of doing it from within Zimbra (instead of Postfix) would be that you wouldn't increase the number of messages in the message store. You'd just increase the number of pointers by one. A simple way of implementing this would be to have a second "shadow" account for each "real" account and have the mail delivered to both. If the real account deletes the message, their pointer goes away but the message is still stored for the shadow. Perhaps you'd never have to reclaim space from the message store either. It sounds neat (at least to me).